Tissue Mechanics- Articular Cartilage

What are the three types of cartilage, and where is type commonly found

elastic- found in epiglottis, larynx, external ear. has the most extracellular matrix, very elastic

hyaline- primary component of articular cartilage

fibrous- found in IVD and pubic symphysis, meniscus, has the least ECM and most collagen

What are the primary functions of articular cartilage in joints

Covers the articular surface

• distribute joint load over a wider area (shock absorption)

• allow relative movement of the opposing joint surface with minimal friction

• improve fit of articular surfaces

• provide lubrication of articular surfaces

what is the role of chondrocytes in articular cartilage

manufacture, secrete, organize, and maintain the organic component of the extracellular matrix

chondrocytes make up 50% of tissue volume in cartilage. T or F

False: makes up less than 10%

describe the structure and function of proteoglycans and their relationship with water in the cartilage matrix

Proteoglycans are large macromolecules composed of a core protein and glycosaminoglycan (GAG) side chains that provide compressive strength and hydration to the cartilage matrix. They attract and retain water, contributing to the cartilage's ability to withstand mechanical loads and maintain its shape.

aging causes what to water? carb to protein ratio?

aging cause the water content and carb/protein ratio to decrease

describe the different zones of articular cartilage and their relationship with cartilage

Superficial zone: densely packed fibers randomly woven in parallel planes to the AC, lowest concentration of PG, resists tensile component of compressive load

Middle zone: greater distances between the collagen, highest concentration of PG; workhorse of cartilage

Deep zone: the fibers come together forming larger, radially oriented fiber bundles, cross the tidemark insert on calcified cartilage and subchondral bone

deformation of cartilage is controlled by what

controlled by PGs

how does articular cartilage handle compressive loads

fluid flows out of collagen, which leads to increased concentration of PGs, which leads to increased negative charge, which leads to attracting water (stiffens the tissue)

what are the keys to resisting compressive loads

The Donnan osmotic swelling pressure associated with the tightly packed anionic group

the bulk stiffness of the collagen PG complex

what is weeping and why is it important for cartilage underload

Process of moving fluid in and out due to osmotic pressure

The tissue is very permeable, it is iversely propotional to the frictional drag fluid flow

the permeability changes in magnitude, and rate of compression loading. Permeability decreases exponentially while load increases and rate increases these changes are also important for joint lubrication

discuss the viscoelastic properties of articular cartilage, including creep, stress relaxation, and hysteresis

Creep- only weeping occurs, takes hours to reach relative equilibrium during creep and stress relaxation

Stress relaxation: weeping occurs initially followed by fluid redistribution

Hysteresis: takes more reps for hysteresis to reduce but area between the cirve is not any bigger than ligament/tendon

describe the differences between fluid film and boundary layer lubrication

fluid film- first responder to compressive loads, especially fast rates of loading. overtime the layer thins out with pressure application leaving high load areas unprotected, most important for nutrition of AC allows nutrients in and out

boundary layer- monolayer of lubrication directly on top of AX, handles high loads, low speeds, and long duration, prevents surface to surface contact and eliminates most of the surface wear, dependent of chemical properties, can reduce friction 3-6 times, best coefficient of friction of all lubricating systems

which layer of film is important fofr letting nutrients in and out of cartilage

fluid film

how do lubrication mechanisms shift during activity

early on in activity- fluid film

sustained loading activity- boundary film

what are interfacial wear and fatigue wear in the context of cartilage

interfacial- interaction of surfaces related to friction

fatigue- related to deformation over time under load

how do partial-thickness and full-thickness cartilage tears differ in terms of repair potential

Partial- does not penetrate subchondral bone, therefore will not repair spontaneously, poor to no healing

full- penetrate the subchondral bone, ability to repair due to bleeding

what are common causes of articular cartilage injuries in children versus adults

Children- acute trauma due to sports

Adult- chondral lesions; pain that increases with weight bearing, swelling, loss of ROM, locking or catching, and instability

how does OA impact articular cartilage on a cellular level

dehydrated cartilage degrades the ECM, changing environment may also lead to cell dedifferentiation

compare the effectiveness and risks of steroid injections versus hyaluronic acid injections in treating cartilage injuries

Steroids- make the tissue worse, collagen synthesis is degraded

hyaluronic acid- relatively minor, local discomfort

what are some surgical options for articular cartilage repair, and how do they aim for restore function

synovectomy- removal of surface fibrillation on AC

lavage and debridement- similar to synovectomy

osteochondral autologous transplantation surgery- for focal lesions in articular cartilage

micro-fracturing- essentially create full thickness tears that penetrate the subchondral bone causing bleeding which allows for clot formation

how might exercise help delay the progression of OA

weight bearing and cyclic exercise and below maximum levels

leads to enhanced diffusion of nutrients, increased thickness, increased matrix synthesis

what are the potential role could mesenchymal stem cells plain in cartilage repair

provide increased cell concentration to injured cartilage in the form of new chondrocytes that can increase concentrations of collagen and aggrecan

what are the challenges associated with using man-made or animal derived tissue replacements for damaged cartilage

man-made tissues can rarely accommodate for such a wide array of loading schemes

animal made- can encode with human DNA and therefore would not have to be on immunosuppressants

given the symptoms and diagnosis of a patient with a full thickness cartilage tear, what treatment options would be approproate

Should be non-weight bearing, do OKC strengthening at other joints in chain, move to PROM, then PWB

what precautions would be necessary post-surgery, and how should a PT program be designed for early intervention

Should be NWB with strengthening at surrounding chain joints